Normally, to control the amount of radiation emitted from a hand-held electronic device and absorbed by human body, a proximity sensor (i.e. P-sensor) is additionally provided in the hand-held electronic device at a position of a primary antenna for wireless wide-area network (WWAN) for sensing the approach of a human body to the hand-held electronic device and accordingly actuating a power-reduction protection mechanism to lower the amount of radiation emitted from the device. Further, to ensure accurate sensing of approach, usually two proximity sensors are used by most electronic device manufacturers in their device designs to achieve the purpose of radiation protection.
Please refer to FIGS. 1 and 2. Conventionally, a portable computer or a hand-held electronic device is provided with a primary antenna 10 and two proximity sensors 11. The primary antenna 10 and the proximity sensors 11 are separate elements and must be spaced from one another by a predetermined distance. As shown in FIG. 1, the proximity sensor 11 generally has a substantial size about 10 mm and the primary antenna 10 about 61 mm, and a space of 5 mm between the primary antenna 11 and each proximity sensor 11 is required. Therefore, a total design length as long as 91 mm is required for the primary antenna 10 and the two proximity sensors 11. However, to meet the progress in the wireless communication transmission technology, the current design size of the antenna needs to be miniaturized.
As a result, another type of antenna structure with proximity sensor has been developed. As shown in FIGS. 3 and 4, this type of antenna 20 includes a dielectric substrate 21 and a capacitive proximity sensor 22. The dielectric substrate 21 is provided on two opposite sides with a first patterned conductive layer 23 and a second patterned conductively layer 24, respectively. The first patterned conductive layer 23 and the second patterned conductive layer 24 are located correspondingly to present patterned traces of an inverted-F antenna, and two capacitors 25, 26 are connected to a signal line 27 and a ground line 28, respectively. Further, the first patterned conductive layer 23 and the second patterned conductive layer 24 are respectively coupled via an inductor 29 to the capacitive proximity sensor 22.
Since this type of antenna structure requires two patterned conductive layers, a plurality of capacitors, and a plurality of inductors to work with the proximity sensor to provide the approach sensing function, it still needs improvement in terms of antenna miniaturization.